HARBOR SEAL TRACKING AND TELEMETRY BY SATELLITE

Authors

  • Brent S. Stewart,

    1. Sea World Research Institute, Hubbs Marine Research Center, 1700 South Shores Road, San Diego, California 92109
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  • Stephen Leatherwood,

    1. Sea World Research Institute, Hubbs Marine Research Center, 1700 South Shores Road, San Diego, California 92109
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    • 1

      Current address: Oceans Unlimited, 2146 Fort Stockton Drive, San Diego, California 92103 USA

  • Pamela K. Yochem,

    1. Sea World Research Institute, Hubbs Marine Research Center, 1700 South Shores Road, San Diego, California 92109
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  • Mads-Peter Heide-Jørgensen

    1. Danbiu ApS., Dampfaergevej 8, DK-2100 Copenhagen, Denmark
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      Current address: Greenland Fisheries Research Institute, Tagensvej 135, 2200 Copenhagen N, Denmark.


Abstract

We tested a satellite Platform Transmitter Terminal (PTT) in the laboratory (on a float and on captive seals) and on a free-ranging harbor seal in the Southern California Bight to investigate the utility of satellite telemetry in documenting seals’at-sea behavior and movements. We used records from a microprocessor-based time-depth recorder (TDR) to interpret location and diving records from the PTT. For the free-ranging harbor seal, we obtained at least one uplink during 70% (while the seal was at sea) to 82% (while she was ashore) of satellite passes and at least one location each day. Of 62 locations determined by Service Argos for the free-ranging seal, 20 were verified from TDR records to have been at sea; these indicated that the seal may have ranged up to 48 km from the haul-out site, although most locations were within 5 km. The accuracies of locations calculated when the seal was at sea (±15 km) were substantially less than when it was ashore (±1.5 km), thus limiting at-sea tracking of seals by satellite to rather gross movements. Fewer transmissions were detected and locations calculated when the seal was actively diving than when it was swimming near the surface as it departed from or returned to the haul-out site. Consequently, average dive durations indicated by the PTT were substantially shorter than those calculated from TDR records. Documentation of foraging areas and detailed at-sea movements using satellite technology may not be possible for pinnipeds unless PTT-transmission rates are increased substantially from the 1 per 45 set maximum rate now permitted by Service Argos.

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